1. Field of the Invention
The present invention relates to a mask for depositing a thin film of a flat panel display, and more particularly, to a mask for depositing a thin film of a flat panel display bonding an reinforcing member and a mask pattern unit portion arranged on an opening portion of the reinforcing member, and a method of fabricating the mask.
2. Description of the Related Technology
Organic light emitting devices (OLEDs) that are self-emitting devices have some advantages such as wide viewing angle, high contrast, and fast response speed, and thus, are considered next generation flat panel display devices. The OLED includes an anode, a cathode, and an organic layer having a light emission layer between the two electrodes. The organic layer is formed with a deposition method since the materials are sensitive to humidity and cannot be formed using a general photolithography process.
FIG. 1 is an exploded perspective view of a conventional deposition mask frame assembly for depositing a thin film of a flat panel display device. Referring to FIG. 1, the mask frame assembly is for depositing the thin film such as the organic layer of the OLED.
Referring to FIG. 1, the conventional mask frame assembly 100 includes a pattern mask 110 and a frame 120 supporting the pattern mask 110. The frame 120 includes left and right supporting bars 121 and upper and lower supporting bars 122 for supporting the pattern mask 110, and a single opening portion 123.
The pattern mask 110 is a thin metal plate 111 including a plurality of mask pattern units 112. Here, the pattern mask 110 includes a plurality of mask pattern units 112 so as to fabricate a plurality of unit devices including the OLEDs on a deposition target substrate 130, that is, a motherboard.
The plurality of mask pattern units 112 are arranged corresponding to the unit devices, respectively, and each of the mask pattern units includes a plurality of openings 113 having the same patterns as those of the thin film of the unit device that will be deposited on the deposition target substrate 130. The pattern mask 110 is fixed onto the frame 120 by tensile forces applied from the sides.
When the pattern 110 is fixed onto the frame 120 of a lattice form, the tensile force should be applied evenly and a width of the opening 113 formed on the mask pattern unit 112 of the pattern mask 110 should be maintained within a predetermined tolerance.
A conventional metal thin plate mask of large area, the mask may droop due to the weight of the mask itself even when the mask is fixed on the frame. When the tensile force is applied to the mask in order to prevent the mask from being drooping, the left and right supporting bars 121 of the frame 120 are curved inward and the upper and lower supporting bars 122 are curved convexly to upper and lower directions, or the left and right supporting bars 121 are curved outward and the upper and lower supporting bars 122 are curved inward.
As described above, even when the pattern mask 110 is fixed on the frame 120 with a tensile force applied evenly across its surface, the openings 113 of the mask pattern unit 112 are distorted, and thus, the electrode pattern (not shown) of a unit device formed on the substrate is inconsistent with the desired opening portion 113 of the mask pattern unit 112.
In order to solve the above problems, Korean Laid-open Patents No. 2003-0046090 and No. 2003-0093959 disclose a mask frame assembly for depositing a thin film of an OLED, in which a pattern mask fixed on the frame is divided into a plurality of unit pattern masks, and both ends of the divided unit pattern mask are fixed to the frame while under tensile stress.
In addition, the conventional pattern mask 110 forms the mask pattern unit 112 as a metal thin plate etched in a photo process using a photosensitive film. The accuracy of the opening and position accuracy of pixels needs to be improved. Therefore, Japanese Laid-open Patent No. 2002-055461 and Korean Laid-open Patent No. 2003-0009324 disclose a method of fabricating a metal mask using an electric plating method.